The present invention relates to an electronic still camera to photograph an optical image of an object using a solid state image sensor.
Differently from optical cameras, electronic still cameras function to receive a still picture of an object by a solid state image sensor to electrically record the still picture.
A conventional electronic camera is shown in FIG. 1. In this electronic camera, when a release switch 8 is turned on for the purpose of photographing an image of an object, a power source (not shown) is turned on. Thus, a solid state image sensor 3, a signal processing unit 4, a recording unit 5, a drive circuit 6, and a control unit 7 are brought into operational condition. A light from the object is converged by a lens 1 in a manner that its optical image is formed on the solid state image sensor 3. A mechanical shutter 2 is opened by an exposure time Tint set in advance at an exposure time setting unit 9. Thus, a pictorial image signal corresponding to the optical image of the object is output to the signal processing unit 4 through the solid state image sensor 3. This pictorial image signal is recorded on a photosensitive recording medium by the recording unit 5.
As just described above, such a conventional electronic still camera employs a mechanical shutter in order to adjust a quantity of light to the solid state image sensor. However, the problem therewith is that the mechanical shutter is expensive because of high precision mechanical parts. In addition, with such a mechanical shutter, an actual exposure time has a large error with respect to the set value. For this reason, when an electronic still camera having a narrow allowed range with respect to exposure time is employed, there occurs the problem that picture quality is degraded because of error of the mechanical shutter.